1. Field of Endeavor
The present invention relates to a measuring apparatus for contactless detection of a distance between a surface of a measurement object and the measuring apparatus, and for simultaneous contactless visual detection of the surface.
2. Brief Description of the Related Art
During the operation of a gas turbine, the most strongly loaded gas turbine blades of the first stage are exposed to hot gas temperatures of above 1400° C. For their protection, these are therefore provided with metallic anti-oxidation layers and, frequently, additionally with ceramic thermal barrier coatings (TBCs). A reliable operation of the turbines over typical intervals can be ensured with the aid of these protective layers even under extreme conditions of use. However, after these intervals it is chiefly the anti-oxidations layers that are consumed, and they no longer offer adequate protection, and so the turbine blade has to be removed and replaced. Because of the high value of such a turbine blade, repair, and thus a recycling of the components, are of great commercial interest. The protective layers can in this case be renewed by firstly removing the consumed layers by a chemical process, and thereupon coating the turbine blades anew. As in the case of the initial production, it is mostly plasma spraying methods that are applied. However, in the case of reconditioning it must be ensured that the original properties of the turbine blades are retained, a key role being played by the internal cooling system of the turbine blade, formed in particular by a complex network of interlinked bores and cooling channels. The restoration of this cooling system is mandatory for the turbine blades strongly loaded by the action of hot gas, in order to be able to release the turbine blades for a further operating interval. However, during the coating of used turbine blades the problem occurs that the originally open cooling air bores are stopped by the renewed coating with the metallic anti-oxidation layer or with the ceramic thermal barrier coating, the result being that the cooling of the turbine blades is drastically worsened and no longer satisfies the operating requirements. For this reason, a special machining process is required for reopening such stopped cooling channels.
The reconditioning process for opening the cooling air bores sealed during the recoating requires the detection of cooling hole positions and orientations. The general result in this case, particularly for conically opening cooling air bores, is depressions that can be detected by means of a distance measuring device.
U.S. Pat. No. 6,667,458 B1 discloses a system and a method for determining a specific distance between a laser system and a surface of a workpiece. The system includes an optical apparatus for focusing the laser beam on the surface of the workpiece, and a mirror device that deflects radiation reflected by the workpiece to a distance measuring device. The distance measuring device can be a conoscope, for example. The distance measuring device is connected to a control device that is designed for positioning the workpiece, that is to say for varying a distance between the measuring system and the workpiece. In this case, the known system detects only a distance between the surface of the workpiece and the measuring system.